1. Field of the Invention
The present invention relates to an intake device of an outboard motor. More specifically, the present invention relates to an intake device supplying combustion air to an engine mounted in an outboard motor.
2. Description of the Related Art
As for an outboard motor provided with an internal combustion engine housed in an engine room formed of an engine cover, there have been known various techniques aimed at preventing water mixed in combustion air from intruding into a combustion chamber. Particularly, in an internal combustion engine mounted in a propulsion unit of an outboard motor or the like, a water intrusion prevention function that is reduced in size and excellent is required.
Conventionally, for example, in an outboard motor disclosed in Patent Documents 1, 2, and the like, for the purpose of achieving improvement of an effect of preventing water intrusion into a combustion chamber in an internal combustion engine and intake air filling efficiency, and so on, it is designed such that when water is mixed in combustion air that has flowed in through an intake port in an intake device, the water is separated from the combustion air in an inversion passage by a centrifugal force.
Concretely, in an outside air intake structure of an outboard motor having an outside air intake port provided at the rear of an upper portion of an engine cover covering an engine, there are included air intake ducts fixedly provided on an engine side and air intake guides that are brought into a state of being connected to the air intake ducts when an engine cover is attached to the outboard motor and guide outside air taken in through the outside air intake port to the air intake ducts, and it is constituted such that the outside air taken in through the outside air intake port is guided to a lower portion in the engine cover through the air intake guides and the air intake ducts. Further, it is suppressed that heated air flows into an engine room through an intake port of an intake passage, and a rise in temperature of the combustion air is suppressed, resulting in that improvement of filling efficiency is achieved.
[Patent Document 1] Japanese Laid-open Patent Publication No. 2007-8416
[Patent Document 2] Japanese Laid-open Patent Publication No. 2008-88881
However, the air taken into the engine cover flows in the immediate vicinity of the high-temperature engine to be warmed up, and then is sucked into a throttle body to be supplied to a combustion chamber. Filling efficiency (volumetric efficiency) of the high-temperature sucked air is poor, and problems that the high-temperature sucked air affects combustion efficiency, and further fuel efficiency, and so on are caused.
Furthermore, as disclosed in Patent Document 1, in the outboard motor of this type, normally the outside air intake port in an outside air intake space formed by an exterior cover opens rearward, namely in a direction opposite to a forward traveling direction of the outboard motor. In such an exterior cover structure, as for taking in air in particular, air is taken in in a manner to go against the flow of air flowing outside the outboard motor. In such a way of taking in intake air, intake resistance is caused to deteriorate intake efficiency, resulting in that engine output is reduced.
On the other hand, in order to improve the intake efficiency, as far as the above point is concerned, it is possible to provide the outside air intake port to be directed forward. However, when the outside air intake port is disposed to be directed forward as above, water splashes and so on get in through the outside air intake port while a craft is traveling, and thus it is substantially impossible to fabricate such an intake structure.